Accurate measurement of photon beam position and profile is crucial for beamline users to achieve precise alignment and efficient utilization of the desired photon beam. In low-emittance storage rings, however, the power density of the photon beam has increased, making it challenging for conventional profile monitors such as wire scanners and scintillating screens to withstand the high power without damage. Here, we present the development of an Ionization Profile Monitor (IPM) capable of robustly measuring the photon beam position and enabling non-destructive beam profile measurement. A noble gas environment was designed to ensure sufficient ionization signal strength, and a defocusing electrode structure was introduced to fully utilize the relatively large active area of the readout system. Since the magnification induced by the defocusing field depends on the vertical position, we proposed a calibration method to correct for the resulting non-linearity. Finally, we present the results from prototype testing, including the measured position accuracy and the point spread function analysis.

Information on the longitudinal phase space (LPS) is essential for tuning injectors that deliver a few-femtosecond electron bunches to beam–plasma interaction experiments and ultrafast diffraction facilities. Direct time–energy characterization, however, is challenging due to the limited resolution of conventional diagnostics. To address this, we apply a tomographic algorithm that uses a booster cavity and a downstream dipole spectrometer to indirectly reconstruct the LPS. A phase scan of the booster cavity adjusts the longitudinal chirp, while the dipole converts the correlated energy spread into a transverse distribution on a screen. An iterative algorithm then retrieves the time–energy distribution. Particle tracking simulations confirm that the method successfully reconstructs the LPS structure. Our next step is to verify the technique on the actual beamline, compare the LPS measured using an RF deflecting cavity with the reconstructed distribution, and use the results to guide injector tuning. We also discuss the potential application of the LPS tomography algorithm developed in this study to non-relativistic ion beams, using a re-bunching cavity and a bunch shape monitor.